Key Penrith Panthers forward Viliame Kikau was helped from the field in the opening minutes of Saturday's trial against the South Sydney Rabbitohs with a knee injury.

The powerful second-rower's right knee appeared to give way as he was bent backwards before copping the weight of a three-man tackle on the greasy Redfern Oval turf.

Kikau gingerly rose to his feet and played the ball but slumped back to all fours in obvious pain. He was then assisted up the tunnel.

Very limited video, but with direction of contact worry for Viliame Kikau right high/medial ankle injury as player came down on back/outside of leg. Potential for knee injury there (MCL/ACL) but less likely, appeared more ankle involved. Struggled to bear weight coming off pic.twitter.com/E9hoR0J6PM